1. Technical Field
The present invention relates to a liquid ejecting apparatus such as an ink jet printer and a method of controlling the liquid ejecting apparatus, and more particularly, to a liquid ejecting apparatus capable of controlling ejection of a liquid by applying an ejection driving pulse to a pressure generation unit and a method of controlling the liquid ejecting apparatus.
2. Related Art
A liquid ejecting apparatus is an apparatus which includes a liquid ejecting head having nozzles ejecting a liquid and ejects various kinds of liquids from the liquid ejecting head. A representative example of the liquid ejecting apparatus is an image printing apparatus such as an ink jet printer (hereinafter, simply referred to as a printer) which includes an ink jet print head (hereinafter, simply referred to as a print head) as a liquid ejecting head and prints an image or the like by ejecting and landing liquid-like ink from nozzles of the print head on a print medium (landing target) to form dots. In recent years, the liquid ejecting apparatus has been applied not only to the image printing apparatus, but also various manufacturing apparatuses such as an apparatus manufacturing a color filter such as a liquid crystal display.
For example, a printer includes a nozzle row (nozzle group) in which a plurality of nozzles are arranged. In the printer, an ejection driving pulse is applied to a pressure generation unit (for example, a piezoelectric vibrator or a heating device) to drive the pressure generation unit, and a pressure variation is applied to a liquid in a pressure chamber to eject the liquid from the nozzles communicating the pressure chamber. In a printer using a piezoelectric vibrator as a pressure generation unit, in general, ink is ejected from nozzles by first expanding a pressure chamber preliminarily (expansion step), holding the expansion state for a given time (hold step), and then rapidly contracting the pressure chamber (contraction step) to pressurize the ink in the pressure chamber.
FIG. 7 is a diagram for explaining flying of ink droplets when ink is ejected by a known printer. More specifically, FIG. 7 is a diagram illustrating a case where the ink is ejected toward a print medium from the respective nozzles of a nozzle row, when viewed from a direction (transverse direction) intersecting the flying direction of the ink. In the drawing, an upper straight line indicates a nozzle surface of the print head and a lower straight line indicates a print surface of the print medium. The nozzles of #1 to #36 are illustrated among all of the nozzles (for example, the nozzles from #1 to #180) of the nozzle row.
In such a kind of printer, the rear end portion of a preceding main liquid droplet is separated from the main liquid droplet and becomes a satellite liquid droplet in some cases. In particular, when a liquid with a viscosity higher than that of aqueous ink used in a known printer, for example, a liquid with a viscosity of, for example, 8 mPa·s or more is ejected, satellite liquid droplets have a tendency to occur more easily. In a configuration in which printing is executed while print head is moved relative to a print medium, the landing positions of the main liquid droplet and the satellite liquid droplet may be distant from each other. A difference between the landing positions of the main liquid droplet and the satellite liquid droplet may cause deterioration in the quality of a printed image.
In order to resolve this problem, for example, there has been suggested a configuration in which a main liquid droplet is ejected in a contraction step by a first waveform component, and then a pressure chamber is expanded by a second waveform component with the ejection of the main liquid droplet at a time, at which a meniscus is moved toward the pressure chamber, depending on the inherent vibration of the ink in the pressure chamber (re-expansion step). Then, in this configuration, pressure variation by the expansion of the pressure chamber is superimposed in the vibration of the meniscus, the vibration is oscillated, the flying speed of the satellite liquid droplet flying after the main liquid droplet is increased by the oscillation (for example, see JP-A-2006-142588). In this way, by increasing the flying speed of the satellite liquid droplet, the landing positions of the main liquid droplet and the satellite liquid droplet on the print medium can be closer to each other.
In the configuration disclosed in JP-A-2006-142588, however, the pressure chamber is contracted in one motion from the maximum volume to the minimum volume in the contraction step. Therefore, since the flying speed of the main liquid droplet is increased and timing of the re-expansion step after the contraction step is measured, the satellite liquid droplet is ejected after a pause from the ejection of the main liquid droplet. For this reason, the satellite liquid droplet may not follow the main liquid droplet. Therefore, a problem may still arise in that the difference between the landing positions may occur on the print medium.